The survival of amphipods in sediment bioassays was compared to the induction of ethoxyresorufin-O-deethylase (EROD) activity in speckled sanddabs (Citharichthys stigmaeus) to investigate the relative importance of physical and chemical characteristics of sediment in toxicity bioassays. Sediments from San Francisco Bay containing 1-30 ppm (dry) of polynuclear aromatic hydrocarbons (PAHs), 3-20 ppb (dry) of polychlorinated biphenyls (PCBs) and variable concentrations of several trace elements were used in separate exposure assays for sanddabs (60 d) and the amphipod Eohaustorius estuarius (10 d). A highly significant correlation (r2 = 0.90, p < .001) was documented between EROD activity in the sanddabs and Eohaustorius survival for all treatments. The accurate prediction of amphipod survival by the contaminant exposure biomarker in the fish is consistent with the contention that contamination, rather than physical characteristics of the sediments, is the cause of amphipod mortality. This result supports the use of these bioassays to screen sediments for ecologically significant contaminant concentrations.